The present invention relates to an improved nasal mask for delivering positive air pressure to the nasal passages to facilitate treatment of breathing disorders such as sleep apnea, ventilation difficulties or anesthetic gas administration.
Obstructive sleep apnea is caused by obstruction of the upper airway during sleep which results in the absence of airflow through the nose or mouth for at least 10 seconds. Obstructive sleep apnea episodes are usually most severe during periods of REM (Rapid Eye Movement) sleep, when muscle tone is inhibited. The upper airway then narrows as a result of the relaxation of a number of muscles. The suction pressure of inspiration then causes further narrowing or collapse of the airway. The lack of airflow causes the oxygen level in the blood to drop causing arousal which then restores upper airway muscle tone allowing normal breathing.
Heavy snoring and daytime sleepiness are the most common symptoms associated with obstructive sleep apnea syndrome. Other complaints include night-time thrashing, sleep walking, enuresis, disorientation, personality changes, intellectual deterioration, sexual dysfunction, hypnagogic hallucinations, automatic behavior and morning headaches. The prevalence of episodes of obstructive apnea and the frequency of occurrence increase with age. Men are much more commonly affected than women and nearly 50% of elderly men have 20 or more apneic episodes each night. Other known risk factors include obesity, chronic alcoholism, chronic obstructive pulmonary disease and post-menopausal state. Altogether more than 30,000 patients are treated each year for obstructive sleep apnea.
The most effective and frequent therapy for obstructive sleep apnea is application of continuous positive airway pressure (CPAP). For such therapy, a patient is fitted with a tight fitting nasal mask connected through an airway to a blower which supplies air at a slight positive pressure to the nasal passages. The application of the slight positive pressure is immediately effective in reversing airway obstruction in most patients with obstructive sleep apnea. Although the therapeutic results of nasal CPAP are often dramatic and immediate, it is only effective when used properly and on a regular basis. Failure to apply nasal CPAP for even a single night results in recurrence of hypersomnolence the next day.
Problems associated with wearing existing masks or positive airway pressure delivery systems during periods of attempted sleep are sufficient to deter many patients from continuing CPAP therapy. Some problems include excessive noise and irritation resulting from leaks around improperly fitting masks or general discomfort caused by the design of the mask or the CPAP delivery system. Leakage of air between the mask and the face often allows air to blow on the eyes which wakes the patient and/or substantially irritates the eyes.